The present invention relates to xe2x80x9cthrow awayxe2x80x9d meltblown fibrous sorbent media of thermoplastic fibers and, in particular, to meltblown fibrous sorbent media of thermoplastic fibers which are especially suited for absorbing oil or water and other liquids and the method of making such sorbent media.
Fibrous sorbent media made of thermoplastic fibers are used for many clean up applications including but not limited to: cleaning up oil spills on water; cleaning machinery, engines and other equipment; cleaning up oil, water, grease or other liquids from floors and other surfaces; etc. Typically, these fibrous sorbent media are intended to be properly discarded after only one use or only a few uses.
Fibrous polypropylene sorbent media is particularly well suited for such tasks. For example, fibrous polypropylene sobrbent media has an affinity for oil and is hydrophobic. Thus, fibrous polypropylene sorbent media will soak up or absorb oil without absorbing water and can be used effectively to clean up oil spills on water. When the fibers of fibrous polypropylene sorbent media are treated or coated with a surfactant, the media will absorb water and other similar liquids. Thus, when treated with a surfactant, fibrous polypropylene sorbent media can be used to clean up water and other liquids in addition to oil.
Previously, the process for producing the fibrous sorbent media manufactured and sold by Johns Manville International, Inc., has essentially included three processes. In the first process, a thin meltblown tightly bonded cover stock is formed having a basis weight of about 0.75 oz/yd2 or another cover stock, such as but not limited to a spun bond cover stock is formed. In the second process an air-laid, non-woven mat or fibrous layer of loose lofty randomly oriented meltblown thermoplastic fibers, e.g. polypropylene fibers having a mean diameter of about 15 microns, and of the required thickness is formed. In a third process a heated pin or calendar roll collates a layer of cover stock onto each major surface of the mat or fibrous layer and, through the heated pins of a pin or calendar roll, heat point bonds the layers of cover stock to the major surfaces of the mat. The resulting product is a fibrous sorbent media laminate with a fibrous core layer of loose lofty fibers encapsulated between two surface layers of cover stock that are heat point bonded to the fibrous core layer. The loose fibers within the media provide an effective surface area for good liquid absorption and the layers of cover stock provide the laminate with the required tensile strengths and abrasion resistance. The heat point bonding of the layers of cover stock to the fibrous core layer provides the fibrous sorbent media with added integrity and improves the xe2x80x9chandle-abilityxe2x80x9d of the product. Fibrous thermoplastic sorbent media laminates, such as the sorbent media just described, provide good liquid absorption for many applications. However, since these sorbent media are primarily used for applications where the sorbent media is discarded after only one use or only a few uses, there has remained a need for fibrous thermoplastic sorbent media, with equal or better liquid absorption and abrasion resistance properties, that can be more economically produced.
The fibrous sorbent media of the present invention and the method of making the fibrous sorbent media of the present invention provide fibrous sorbent media that have liquid absorption and abrasion resistance properties which are equal to or greater than the fibrous sorbent media laminates of Johns Manville International Inc. discussed above and media which can be produced more economically (e.g. cost savings of up to 30% to 40%) than the fibrous sorbent media laminates of Johns Manville International Inc. discussed above. The sorbent media of the present invention is made of thermoplastic fibers having a mean diameter between about 0.5 microns and about 25 microns; has a weight between about 2 oz/yd2 and about 25 oz/yd2; a thickness typically between about {fraction (1/20)} of an inch and about xc2xd of an inch; a lofty fibrous core; and first and second major surfaces with thin, relatively tough, tear and abrasion resistant, integral skins thereon. The skins are liquid permeable and permit liquids, such as but not limited to oil and water, to pass easily through the skins for absorption in the fibrous core of the sorbent media. The abrasion resistant skins add to the tensile strength of the sorbent media; help to keep the sorbent media from tearing apart in use; and prevent or greatly reduce the loss of fibers from the sorbent media in use, especially when the sorbent media is used for wiping machinery, floors, etc.
The abrasion resistant integral skins of the mat are formed by melting fibers at and immediately adjacent the major surfaces of the non-woven mat to form thermoplastic melt layers which are subsequently solidified into the abrasion resistant skins on the major surfaces of the mat. For many applications, the thermoplastic fibers of the mat are point bonded together at spaced apart locations to increase the integrity of the mat and, preferably, increase the thickness or loft of the mat adjacent the point bonded locations.
The method of forming the sorbent media of the present invention, e.g. on an on-line process, includes: air laying thermoplastic fibers having a mean fiber diameter between about 0.5 microns and about 25 microns to form a non-woven mat; melting the thermoplastic fibers at and immediately adjacent the major surfaces of the mat to form thermoplastic melt layers on the major surfaces of the mat; subsequently cooling the thermoplastic melt layers to form thin, integral thermoplastic, liquid permeable skins on the major surfaces of the mat; and, normally, point bonding the thermoplastic fibers of the mat together at spaced apart locations to increase the integrity of the mat and preferably, increase the loft of the mat adjacent the point bonds by displacement of some of the thermoplastic fibers from the locations of the point bonds.
The thermoplastic fibers at and immediately adjacent the major surfaces of the mat can be melted to form a thermoplastic melt layer on the major surfaces of the mat by flame treating, infrared treating or corona treating the surfaces of the mat. However, preferably, the thin, integral skins are formed on the major surfaces of the mat by passing the mat between a pair of heated nip or calendar rolls with smooth surfaces. Preferably, the major surfaces of the mat on which skins are being formed are pressed against the heated surfaces of the nip or calendar rolls by compressing the mat between the pair of heated nip or calendar rolls. It is believed that the compression of the mat brings more fibers into contact with the heated surfaces of the nip or calendar rolls and increases the density of the mat at and adjacent the heated surfaces of the nip or calendar rolls for better heat transfer from the nip or calendar rolls into the thermoplastic fibers of the mat. The result is a better melting of the thermoplastic fibers at and immediately adjacent the major surfaces of the mat to form melt layers on the major surfaces of the mat that are subsequently cooled and solidified to form the relatively tough, tear and abrasion resistant, liquid permeable, integral skins. When skins were formed on major surfaces of a mat without compressing the mat between heated nip or calendar rolls, the quality of the skin formed was considerably inferior to the skins formed by compressing the mat between heated nip or calendar rolls.
The compression of the mat between a pair of heated nip or calendar rolls, decreases the thickness of the mat. Accordingly, the thickness and resiliency of the non-woven mat being introduced into the skin forming station of the process line must be sufficient to accommodate the decrease in thickness caused by the skin forming operation without permanently decreasing the thickness and absorbent properties of the mat below acceptable levels.
Preferably, the point bonds are formed using the heat generated solely from the pressure exerted on the fibers by the pins of an unheated pin or calendar roll assembly. While the point bonds can be formed using heated pins of a heated pin or calendar roll assembly, the heat from the heated pins of such an assembly causes the thermoplastic fibers contacted and adjacent the heated pins to shrink down to form a point bond. When using unheated pins to form the point bonds, at least some of the thermoplastic fibers present along the paths of pins through the mat are pushed away or displaced from the paths of the pins thickening the mat adjacent the point bonds and leaving only a thin layer of thermoplastic fibers to form the point bonds through the heat generated by the pressure applied by the pins to the remaining thin layer of thermoplastic fibers. Thus, rather than decreasing the thickness of the mat which would decrease the absorption properties of the mat, the use of unheated pins maintains or in effect increases the thickness of the mat while increasing the integrity of the mat through the point bonding of thermoplastic fibers within the mat.